Rice false smut, caused by Ustilaginoidea virens, is a serious disease of rice worldwide, severely reducing the quantity and quality of rice production. The conserved fungal velvet proteins are global regulators of diverse cellular processes. We identified and functionally characterized two velvet genes, UvVEA and UvVELB, in U. virens. The deletion of these genes affected the conidiation of U. virens but had no effect on the virulence of this pathogen. Interestingly, the ΔUvVEA mutants appeared in the form of smaller false smut balls with a reduced number of chlamydospores compared with the wide-type strains. In addition, the deletion of UvVEA affected the expression of some transmembrane transport genes during chlamydospore formation and rice false smut balls development. Furthermore, the ΔUvVEA mutants were shown to be defective in the utilization of glucose. These findings proved the regulatory mechanism underlying the formation of rice false smut balls and chlamydospores and provided a basis for the further exploration of the mechanism of these processes.

Rice blast, caused by Pyricularia oryzae, is one of the most destructive rice diseases worldwide. Using resistant rice varieties is the most cost-effective way to control the disease, and it is crucial to analyze the resistance level and the resistance genes distribution of the main varieties. In this study, we collected 119 rice main varieties in Jiangsu province and evaluated the resistance to leaf and panicle blast and found that indica rice was more resistant to rice blast than japonica rice. Moreover, we detected the distribution of 14 resistance genes (R genes) in the 119 varieties. The distribution frequencies of three R genes, Pish, Pit, and Pia, were higher than 80%, and the Pigm had the lowest distribution frequency (1.68%), followed by Pi2 (15.18%) and Pi5, Piz-t (24.37%). Combined with the multiple stepwise regression and the resistance contribution rate, eight major R genes Pita, Pi5, Pi9, Pib, Pb1, Pikm, Piz-t, and Pi2 significantly affected the resistance of rice, and we also found that six gene combinations with 100% resistance contribution rate could effectively increase the resistance of rice varieties. In summary, monitoring the resistance level of rice varieties and analyzing their resistance genes were beneficial for rice resistance breeding.

Rice false smut, caused by the plant pathogenic fungus Ustilaginoidea virens, is widespread in rice-growing regions globally, severely compromising rice quality and production. Employing Bacillus spp. to control rice false smut represents an effective and environmentally sustainable strategy for disease management. The lipopeptides produced by Bacillus velezensis Jt84 demonstrated robust inhibitory effects against U. virens, resulting in abnormal mycelial morphology and spore germination. Iturins were identified as essential for the antifungal activity against U. virens, as confirmed by mutagenesis experiments that suppressed iturin biosynthesis. The surfactin-deficient mutant exhibited inhibitory effects against U. virens comparable to the wild-type, indicating that the absence of surfactins did not diminish its antifungal activity. Both the Jt84∆srf and Jt84∆itu mutants displayed reduced biofilm formation capabilities compared to the wild-type, with the Jt84∆srf mutant being particularly impaired and unable to form a complete biofilm. Regarding swarming motility, the ∆srf mutant exhibited a significant reduction compared to the wild-type, whereas the Jt84∆itu mutant showed a modest increase. Colonization experiments revealed that the Jt84∆srf mutant strain had significantly lower colonization on rice leaf surfaces than the wild-type strain, highlighting the critical role of surfactins in the colonization of B. velezensis Jt84 on rice leaves. In conclusion, our research demonstrated that surfactins and iturins have distinct functionalities and act synergistically to contribute to the biocontrol of rice false smut in B. velezensis Jt84. This synergy is achieved through their potent antifungal effects, biofilm formation, and successful colonization.

The mitogen-activated protein kinase (MAPK) signaling pathways regulate diverse cellular processes and have been partially characterized in the rice false smut fungus Ustilaginoidea virens. UvSte50 has been identified as a homolog to Saccharomyces cerevisiae Ste50, which is known to be an adaptor protein for MAPK cascades. ΔUvste50 was found to be defective in conidiation, sensitive to hyperosmotic and oxidative stresses, and non-pathogenic. The mycelial expansion of ΔUvste50 inside spikelets of rice terminated at stamen filaments, eventually resulting in a lack of formation of false smut balls on spikelets. We determined that UvSte50 directly interacts with both UvSte7 (MAPK kinase; MEK) and UvSte11 (MAPK kinase kinase; MEKK), where the Ras-association (RA) domain of UvSte50 is indispensable for its interaction with UvSte7. UvSte50 also interacts with UvHog1, a MAP kinase of the Hog1-MAPK pathway, which is known to have important roles in hyphal growth and stress responses in U. virens. In addition, affinity capture–mass spectrometry analysis and yeast two-hybrid assay were conducted, through which we identified the interactions of UvSte50 with UvRas2, UvAc1 (adenylate cyclase), and UvCap1 (cyclase-associated protein), key components of the Ras/cAMP signaling pathway in U. virens. Together, UvSte50 functions as an adaptor protein interacting with multiple components of the MAPK and Ras/cAMP signaling pathways, thus playing critical role in plant infection by U. virens.

The rice blast, caused by the hemibiotrophic plant pathogen Magnaporthe oryzae, is a devastating disease that threatens rice crop production worldwide. The molecular interactions that underlie the rice-M. oryzae interaction have received much attention. However, genome-wide research focusing on alternative splicing (AS) has not been well-studied in rice—M. oryzae interactions. AS in plants leads to diverse proteomes without an expansion in gene numbers to regulate cellular processes during abiotic or biotic stress. The Pi21 gene negatively regulates rice resistance to M. oryzae infection, and thus the Pi21-RNAi silenced transgenic line (#241) exhibits partial but durable resistance. We compared the AS landscape in #241 and “Nipponbare” (Nip) during interacting with M. oryzae Guy11, and the alternative 3′ splice-site (A3SS) is the most common AS type. GO enrichment analysis of #241-specific differentially alternatively spliced genes (DASGs) revealed that WRKY transcription factors (TFs), bHLH TFs, F-box protein with leucine rich repeats, AAA-type ATPase, and protein kinase were enriched in the GO terms “response to jasmonate acid (JA)” and “ethylene (ET)” at 24 h post-inoculation (hpi). At 48 hpi, one #241-specific DASG, ubiquitin gene (Os08g0295000), was predicted to be involved in endoplasmic reticulum (ER) stress. In silico analysis combined with PCR amplification confirmed that multiple isoforms are produced by Os08g0295000 and a skipped exon (SE) event results in isoform switching during interaction with M. oryzae. Protein–protein interaction (PPI) network analysis predicted that Os08g0295000-encoding proteins may interact with SNARE protein Q9LGF8 (Uniprot ID) to cooperatively regulate rice’s response to M. oryzae. This study uncovered the AS profile of rice in response to M. oryzae, which will help to explore the linkage between AS and durable rice resistance.

Rice blast, caused by Pyricularia oryzae, is one of the most destructive rice diseases worldwide. It is essential to understand the population structure and race distribution of P. oryzae for the prevention and control of rice blast. This study collected 1584 isolates across Jiangsu province from 2003 to 2017 to determine race diversity, common and dominant race structures, and resistance profiles using eight parameters from the Chinese differential cultivars (CDC) entries. Race diversity analysis indicated that the race diversity of 1584 isolates in Jiangsu province increased from 2003 to 2006 and fluctuated steadily from 2007 to 2017. Common race structure analysis showed that the common race structure of the isolates fluctuated wildly on an annual basis. Moreover, the race ZG1 was the dominant race, suggesting that the most commonly grown rice varieties in Jiangsu are highly adaptive to race ZG1. In addition, due to a higher level (>85%) of resistance to the population of isolates from 2003 to 2017, Tetep may be conformed as the most promising donor of blast resistance for resistance breeding in Jiangsu province. In summary, it is beneficial to control rice blast by continuous monitoring of the population structure and distribution of P. oryzae with the monogenic germplasm entries and by maintaining a diversity of rice varieties.